Apparatus and methods for substantial planarization of solder bumps

ABSTRACT

Apparatus and methods for substantial planarization of solder bumps. In one embodiment, an apparatus includes a planarization member engageable with at least some of the plurality of outer surfaces to apply a planarization action on one or more of the outer surfaces to substantially planarize the plurality of outer surfaces, and a securing element to securely position the bumped device during engagement with the planarization member. Through application of “additive” and/or “subtractive” processes, the solder balls are substantially planarized. In alternate embodiments, the planarization member includes a cutting tool and the planarization action comprises a milling action; or the planarization member includes a heated platen and the planarization action comprises a thermo-mechanical deformation action; or the planarization member includes an abrasive surface and the planarization action comprises a grinding action; or the planarization member includes a chemical solution and the planarization action comprises a chemical reaction; or the planarization member includes a solder deposition device and the planarization action comprises a solder. In a further embodiment, an apparatus includes a load device to urge the at least some outer surfaces of the bumped device into engagement with the planarization member.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.09/370,498, filed Aug. 9, 1999, now U.S. Pat. No. 6,267,650.

TECHNICAL FIELD

The present invention relates to apparatus and methods for substantialplanarization of solder bumps for use in, for example, testing andfabrication of chip scale packages, bumped die, and other similardevices.

BACKGROUND OF THE INVENTION

The demand for smaller packaging of electronic components continues todrive the development of smaller chip scale packages (CSP's), bumpeddie, and other similar devices having solder bumps, ball grid arrays(BGA's), or the like. As a result, spacing (or “pitch”) between adjacentsolder balls on bumped devices has steadily decreased. Typicalrequirements for ball pitch have decreased from 1.27 mm to 0.5 mm orless, and the trend continues.

FIG. 1 is a side elevational view of a typical bumped device 10 (CSP,bumped die, etc.) mounted on, for example, a printed circuit board 20.The bumped device 10 includes a plurality of solder balls 12 attached toa plurality of ball pads (not shown) which are formed on a die 14. Eachsolder ball 12 has an outer edge 16 that aligns with a correspondingcontact pad 18 on the printed circuit board 20. A conductive lead 22 isattached to each contact pad 18. Ideally, the outer edge 16 of eachsolder ball 12 contacts the corresponding contact pad 18 during assemblyof the bumped device 10 with the printed circuit board 20, completingthe electrical circuit between the conductive leads 22 and the die 14.

The height and width of the solder bumps 12 on the bumped device 10 arenot precisely uniform. Variation of the solder bump height and widthdepends on several factors, including variation in size of the originalunattached solder balls, variation in the sizes of the ball pads, anddifferences in the attachment process.

As the demand for smaller packaging continues, however, CSP reliabilityconcerns arise. For example, using typical manufacturing methods andsolders, the nominal variation between the tallest and shortest balls(shown as the distance d on FIG. 1) is presently about 60 microns (μm).Therefore, when the device 10 is placed on a flat surface resting on thesolder balls, the three tallest balls or bumps define the seating planeof the device, and the smaller balls do not touch the correspondingcontact pads of the printed circuit board or test interposer.

During assembly, and in some cases during testing, a moderatecompression force may be applied to the bumped device 10 to drive theouter surfaces 16 of the solder balls 12 into contact with the contactpads 18 of the printed circuit board or test interposer 20. Typically,the compression force needed to bring the solder bumps into contact withthe contact pads varies between 30 grams and 2000 grams depending uponthe manufacturing or test process involved. The applied compressionforce should be kept to a minimum, however, because larger forces maydamage the circuitry of the die 14, the CSP solder balls, or the testinterposer.

One approach to the problem is to mount the contact pads 18 of the testinterposer 20 on micro-springs. As the tallest solder bumps engage themicro-spring mounted contact pads, the micro-springs axe compressed,allowing the shorter solder balls to engage the corresponding contactpads. Numerous micro-spring contact pad models are available as shownand described in Robert Crowley's article in Chip Scale Review publishedMay 1998, p. 37, incorporated herein by reference. Although desirableresults may be achieved with such devices, micro-spring mounted contactpads 18 are very expensive, relatively difficult to maintain, and mayexcessively damage the solder ball itself.

During assembly of the bumped device 10 with the printed circuit board20, some of the shorter solder balls may not solder to their associatedcontact pads during the reflow process. In the past, to increase thenumbers of solder balls making contact with the contact pads duringreflow, the volume of the solder balls was increased. As packaging sizesand pitch requirements continue to decrease, however, the volume of thesolder balls must be reduced accordingly, and thus, the percentage ofballs that will not attach to the contact pads during reflow increases.Again, if considerable force is applied during assembly, the CSP or theprinted circuit board 20 may be damaged.

SUMMARY OF THE INVENTION

The present invention is directed toward apparatus and methods forsubstantial planarization of solder bumps for use in, for example,testing and fabrication of chip scale packages, bumped die, and othersimilar devices. In one embodiment, an apparatus in accordance with theinvention includes a planarization member engageable with at least someof the plurality of outer surfaces, and a securing element engageablewith the bumped device to securely position the bumped device duringengagement with the planarization member. During engagement with the atleast some outer surfaces, the planarization member applies aplanarization action on one or more of the outer surfaces tosubstantially planarize the plurality of outer surfaces. In oneembodiment, the planarization member includes a cutting tool and theplanarization action comprises a milling action. In another embodiment,the planarization member includes a heated platen and the planarizationaction comprises a thermo-mechanical deformation action. In yet anotherembodiment, the planarization member includes an abrasive surface andthe planarization action comprising a grinding action. Alternately, theplanarization member includes a chemical solution and the planarizationaction comprises a chemical reaction. In yet another embodiment, theplanarization member includes a solder deposition device and theplanarization action comprises a solder deposition.

Alternately, an apparatus may include a planarization gauge thatmeasures a planarization condition of the outer surfaces. Theplanarization gauge may measure the planarization condition before orafter the planarization member is engaged with the outer surfaces.

In a further embodiment, an apparatus includes a load device engageablewith at least one of the bumped device or the planarization member tourge the at least some outer surfaces of the bumped device intoengagement with the planarization member. The planarization memberapplies a planarization action on one or more of the plurality of outersurfaces to substantially planarize the plurality of outer surfaces.

In one embodiment, the planarization member includes a substantiallyflat surface and the load device includes a mass having a weight thaturges the at least some outer surfaces into engagement with the flatsurface to mechanically flatten the surfaces. In another embodiment, theload device includes a fixed surface and a pressurizable vessel, apressure in the pressurizable vessel urging the bumped device away fromthe fixed surface and into engagement with the planarization member. Inyet another embodiment, the load device includes a press engageable withthe bumped device. In still another embodiment, the load device includesa centrifuge engageable with the planarization member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of a bumped device engaged with aprinted circuit board in accordance with the prior art.

FIG. 2 is a side elevational view of the bumped device of FIG. 1 engagedwith a planarization apparatus in accordance with an embodiment of theinvention.

FIG. 3 is a side elevational view of the bumped device engaged with theprinted circuit board of FIG. 1 following substantial planarization ofthe bumps in accordance with the invention.

FIG. 4 is a side elevational view of the bumped device of FIG. 1 engagedwith a device having protruding contacts.

FIG. 5 is a side elevational view of the bumped device of FIG. 1 engagedwith a planarization apparatus in accordance with an alternateembodiment of the invention.

FIG. 6 is a side elevational view of the bumped device of FIG. 1 engagedwith an alternate embodiment of a planarization apparatus in accordancewith the invention.

FIG. 7 is a side elevational view of an alternate embodiment of aplanarization apparatus in accordance with the invention.

FIG. 8 is a side elevational view of another alternate embodiment of aplanarization apparatus in accordance with the invention.

FIG. 9 is a side elevational view of yet another alternate embodiment ofa planarization apparatus in accordance with the invention.

FIG. 10 shows a partial cross-sectional view of still another embodimentof a planarization apparatus in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is generally directed toward apparatus andmethods for substantial planarization of solder bumps for use in, forexample, testing and fabrication of chip scale packages, bumped die, andother similar devices. Many specific details of certain embodiments ofthe invention are set forth in the following description and in FIGS.2-10 to provide a thorough understanding of such embodiments. Oneskilled in the art, however, will understand that the present inventionmay have additional embodiments, or that the present invention may bepracticed without several of the details described in the followingdescription.

FIG. 2 is a side elevational view of a bumped device 10 engaged with aplanarization apparatus 100 in accordance with an embodiment of theinvention. In this embodiment, the planarization apparatus 100 includesa rotating cutting head 102 with a plurality of cutting blades 104. Asecuring element 106 having a recess 108 adapted to receive the bumpeddevice 10 is engaged with the bumped device 10 to secure the bumpeddevice 10 in position during engagement of the solder balls 12 with thecutting head 102. A planarization gauge (or sensor) 109 is positionedproximate the bumped device 10 to measure (or sense) a planarizationcondition of the outer surfaces 16 of the solder balls 12.

As used throughout the following discussion, the term “bumped device”refers not only to the bumped die depicted in FIG. 2, but also to a widevariety of microelectronics devices having solder bumps, includingCSP's, flip-chips, ball grid array (BGA) packages, and micro-BGApackages. Furthermore, the term bumped device is intended herein toinclude multiples or combinations of bumped devices, such as an entirewafer of bumped dice prior to die singulation, or an entire handlingtray containing multiple bumped packages.

In operation, the securing element 106 secures the bumped device 10 inposition for engagement of the bumped device 10 with the cutting head102. As the cutting head 102 is moved along the bumped device 10 (orvice versa), the cutting blades 104 rotate (as indicated by arrow w) andengage the outer surfaces 16 of the tallest solder bumps 12. The cuttingblades 104 perform a planarization action (i.e. subtractive cutting ormilling) on the outer surfaces 16 of one or more of the bumps 12. Afterengagement of the bumped device 10 with the planarization member 100,the gauge 109 may be used to check the outer surfaces 16, 16 a todetermine whether the solder balls 12 are all approximately the sameheight. If the outer surfaces are not planarized to the desiredtolerance, the planarization apparatus 100 may be re-engaged with theouter surfaces 16, 16 a one or more times until the balls aresubstantially planarized.

The terms “planarized” and “planarization” are used throughout thisdiscussion to refer to the fact that the solder balls 12 are made to beapproximately the same height—that is to say, the solder balls projectfrom the bumped device by approximately the same distance or thickness.It is not intended to imply that the outer surfaces 16 of all of thesolder balls 12 are made flat. As shown in FIG. 2, the planarizationapparatus 100 need not engage all of the solder balls 12, and solderballs of different heights are engaged to different degrees. The actualnumber of solder balls engaged by the planarization apparatus 100 willdepend upon the height variation of the balls of the array. Thus, someof the outer surfaces 16 a of the solder balls 12 may be flattened, andsome will remain rounded. Following application of the planarizationaction, the plurality of solder balls on the bumped device will besubstantially (i.e. approximately) the same height, a condition referredto as “substantially planarized.”

In an alternate embodiment, as shown in FIG. 2, a planarization member100A includes a cutting tool 103 that is oriented approximatelyperpendicular to the die 14. The cutting tool 103 may be positioned on acontrollably driven base (not shown) and may be sized to apply aplanarization action on a single solder bump 12. Thus, rather thanflattening a row or group of solder bumps 12 in a batch mode, thecutting tool 103 allows individual solder balls 12 to be selected formilling. The cutting tool 103 could also be used to remove most or allof a damaged ball. The ball could then be replaced by installation of apreformed ball, or by successive deposition of layers of solder using asolder deposition process, as described more fully below.

One may note that the planarization gauge 109 is depicted in FIG. 2 asbeing an optical device that senses the planarity of the outer surfaces16, 16 a, such as the type of laser-based gauges disclosed in U.S. Pat.No. 5,663,797 to Sandhu for detecting the endpoint inchemical-mechanical polishing of semiconductor wafers. The gauge 109,however, may be of any type that is suitable for detecting the heightsof the solder bumps, including feeler gauges that physically contact thesolder bumps or non-contacting capacitative-type height gauges.Alternately, the planarization gauge 109 may be incorporated into eitherthe planarization member 100, 100A or the securing element 106, or byproper control of the planarization member and securing element, thegauge may be eliminated.

It should be noted that the gauge 109 could measure all the balls 12 onthe package 10 and then the planarization member 100, 100A could bedirected to only mill off the “tallest” balls. The balls chosen toreceive the planarization action could be determined by, for example, asoftware program. The software program could accept input signals fromthe gauge 109 and transmit control signals to a controller whichcontrollably positions the planarization member 100, 100A to act on thetallest solder balls 12, thus substantially planarizing the solder ballsin a fully-automated, controlled fashion.

FIG. 3 is a side elevational view of the bumped device 10 engaged withthe printed circuit board 20 of FIG. 1 following substantialplanarization of the outer surfaces 16, 16 a. After engagement with theplanarization apparatus 100, most or all of the outer surfaces 16, 16 aare in contact with the corresponding contact pads 18 on the printedcircuit board 20.

An advantage of substantially planarizing the outer surfaces 16, 16 a ofthe bumped device 10 is that testing of the die 14 is significantlyenhanced. Because the solder balls 12 are brought into contact with thecontact pads 18 with minimal applied force, reliable testing of the diemay be achieved without damaging the circuitry of the die.

Another advantage of substantially planarizing the outer surfaces of thesolder bumps is that expensive micro-spring contact devices areeliminated. Significant cost and maintenance savings may be realizedusing the relatively simple, economical planarization member comparedwith the purchase or fabrication of a test interposer havingmicro-spring mounted contact devices.

Yet another advantage is realized when the substantially planarizedouter surfaces 16 a are engaged with a device 20 a (e.g. printed circuitboard, test interposer, etc.) having protruding or pedestal-shapedcontacts 18 a. FIG. 4 shows the bumped device 10 having substantiallyplanarized solder bumps 12 engaged with a test interposer 20 a havingprotruding contacts 18 a. Without planarization of the solder bumps 12,the height h of the protruding contacts 18 a, would need to be on theorder of 60 μm—the nominal variation between the tallest and shortestballs without planarization (shown as distance d on FIG. 1).

When the outer surfaces of the solder balls are substantiallyplanarized, however, the variation of solder ball heights is reduced sothat the required pedestal contact height is reduced accordingly. Withthe solder balls substantially planarized, the required height of theprotruding contacts 18 a on the test interposer 20 a, for example, isreduced to about 20 μm, which is just enough to penetrate a layer ofsurface oxides on the solder balls for testing of the bumped device 10.By reducing the height requirement of the protruding contacts,substantial savings in manufacturing costs of the protruding contacts isachieved.

FIG. 5 is a side elevational view of the bumped device 10 of FIG. 1engaged with an alternate embodiment of a planarization apparatus 200 inaccordance with the invention. In this embodiment, the planarizationapparatus 200 includes a heated platen 202 having a substantially flatsurface 204 engageable with the outer surfaces 16 of the solder balls12, and a securing element 206 having an aperture 208 therethrough. Thebumped device 10 is securely engaged within the aperture 208 so that thesecuring element 206 secures and positions the device during engagementwith the heated platen 202.

As the heated platen 202 is engaged with the outer surfaces 16, theouter surfaces are heated by the flat surface 204 of the platen.Depending upon the temperature of the platen 202, and the period ofcontact with the platen, the outer surfaces may be softened andmechanically flattened by the flat surface 204, or may be heated untilthe solder sublimates. In either case, these thermo-mechanical actionsperformed by the heated platen 202 on the solder balls 12 substantiallyplanarize the outer surfaces 16 a to an approximately uniform height.

One may note that if temperature of the platen 202 is high enough toliquify the solder, then the platen 202 is preferably made of a materialthat the solder will not wet to. Also, if the platen 202 is removed fromthe ball while the ball is still in a liquid state, then the surfacetension of the ball may cause the ball to reform into its originalundesirable spherical shape. Thus, if the platen 202 temperature issufficient to liquify the solder ball 12, then after the ball has beenliquified and mechanically reformed, it is preferable that the platen202 temperature be reduced while the platen remains in contact with theball 12 until the solder ball solidifies into a substantially planarizedshape.

Although the heated platen 202 is shown in FIG. 5 as only contactingfour of the solder balls 12, it is apparent that the platen may be madeas large or as small as desirable. The platen may, for example, becoextensive with all the balls of the bumped device 10. Alternately, theheated platen may be configured to contact only one ball (or one row) ata time, such as by using a roller, a blade, a squeegee, or otherconfiguration.

Numerous alternate embodiments of planarization apparatus areconceivable. For example, in one alternate embodiment, the planarizationapparatus 200 includes a grinding member 202 having an abrasive surface204 engageable with the outer surfaces 16 of the solder bumps 12. Inthis embodiment, the grinding member 202 is laterally moveable(indicated in FIG. 4 by the double-headed arrow h) with respect to thesolder bumps 12. As the grinding member 202 is moved, the abrasivesurface 204 performs a grinding action on one or more of the bumps 12,thereby substantially planarizing the outer surfaces 16 a.

Alternately, the grinding member may rotate with respect to the bumps ina manner similar to the chemical-mechanical polishing (CMP) devices forplanarization of silicon wafers, including, for example, the typesdisclosed in U.S. Pat. No. 5,738,567 to Manzonie and Akram. The abrasivesurface 204 may be used with a polishing solution that helps to dissolvethe outer surfaces of the solder bumps, or an abrasive slurry thatassists in the physical removal of material from the outer surfaces.Furthermore, planarization apparatus in accordance with the inventionmay be used to planarize the solder balls of flip-chip devices whilestill in whole wafer form, prior to die singulation of the wafer.

In another alternate embodiment, the planarization apparatus 200includes a reactive member 202 having a chemically-coated or wettedsurface 204. As the wetted surface 204 is engaged with the outersurfaces, a chemical action is performed on the solder bumps whichdissolves the outer edges of the tallest bumps, making the bumpsapproximately the same height and substantially planarizing the outersurfaces 16, 16 a. Suitable chemicals for coating or wetting the surface204 for chemically reacting with the solder balls are known in theindustry, as discussed in greater detail below. Many alternateembodiments of securing elements are available, including, for example,those having recesses (FIG. 1), apertures (FIG. 2), pinching mechanisms,clamping mechanisms, or suction mechanisms. In general, all types ofsecuring elements that securely position the bumped device duringengagement with the planarization member are acceptable.

FIG. 6 is a side elevational view of the bumped device 10 of FIG. 1engaged with an alternate embodiment of a planarization apparatus 300 inaccordance with the invention. In this embodiment, the planarizationapparatus 300 has a pair of contact posts 302 that contact the outersurfaces 16 of the solder balls 12, and a solder deposition device 304.The solder deposition device 304 deposits a solder buildup layer 308 onselected solder balls 12. A securing element 306 pinches the substrate14 of the bumped device 10 to securely position the device duringengagement with the solder deposition device 304.

In operation, the contact posts 302 systematically contact the outersurfaces 16 of at least some of the solder balls 12 to determine thehighest solder balls 12. The highest solder balls then define a seatingplane 307. For example, for a two-dimensional array of solder balls, theseating plane 307 may be defined by the three tallest balls or, ifdesired, from the single tallest ball. Similarly, for a single row ofsolder balls, the seating plane 307 may be determined from the twotallest balls or the single tallest ball. Once the seating plane 307 isestablished, the solder deposition device 304 is positioned over each ofthe shorter solder balls and deposits one or more buildup layers ofsolder 308 on each of the shorter balls. The buildup layers 308 aresuccessively applied until the height of each solder ball reaches theseating plane 307 through an “additive” planarization process, and theouter surfaces are substantially planarized.

One may note that the process involving definition of the seating plane307 may be employed equally well with the planarization apparatus thatemploy “substractive” planarization actions, such as the rotating cutteror the heated platen. Furthermore, through combination of various“substractive” and “additive” processes, damaged balls may be partiallyor wholly removed and replaced until the solder balls 12 aresubstantially planarized. Thus, the inventive apparatus and processesmay be used to rework or repair bumped devices 10 with missing ordamaged solder balls.

Although the planarization apparatus 300 is shown in FIG. 6 as havingtwo contact posts 302, it should be recognized that many alternativeways of defining the seating plane 307 exist. For example, theplanarization apparatus 300 may have only a single contact post that isused to sample the heights the solder bumps, or may have a contact postfor each of the solder bumps on the bumped device 10.

Also, the planarization apparatus 300 may have a single, adjustablypositionable solder deposition device 304 as shown in FIG. 6, or manysolder deposition devices, such as one solder deposition device persolder bump. The solder deposition device 304 may include a solder jet,or a solder ball bumper, or other suitable device. Representative,commercially-available devices include the drop-on demand solder jetsystems from MPM Corporation of Franklin, Mass., or the solder ballbumper Model SB²M from Packaging Technologies, GmbH of Germany.

It may also be noted that the seating plane 307 may be defined at anydesired intermediate level that is somewhere between the highest andlowest bumps. In that case, the solder deposition device 304 could beused to build up the heights of the shorter solder bumps 12, whileanother planarization member (e.g. cutting head, heated platen, etc.)could be used to reduce the heights of the taller solder bumps until allof the solder bumps are substantially planarized.

FIG. 7 is a side elevational view of an alternate embodiment of aplanarization apparatus 400 in accordance with the invention. Thisembodiment of the planarization apparatus 400 is suitable for use with,for example, a bumped device 10 a that is capable of withstanding amoderate or larger compression load without sustaining damage. Theplanarization apparatus 400 includes a planarization chuck 402 having asubstantially flat surface 404, and a retaining mass 406 engaged withthe substrate 14 of the bumped device 10 a.

In operation, the bumped device 10 a is positioned with the solder balls12 facing the flat surface 404 of the planarization chuck 402, and theretaining mass 406 is engaged onto the bumped device 10 a. The retainingmass 406 secures the bumped device 10 a into engagement with theplanarization chuck 402, and the weight of the retaining mass 406compresses the solder balls 12 against the flat surface 404, flatteningthe outer surface 16 of some or all of the balls, particularly thetallest balls. The compression caused by the weight of the retainingmass mechanically deforms the outer surfaces 16 a, thereby substantiallyplanarizing the outer surfaces 16, 16 a of the solder balls. Thus, theplanarization member 400 advantageously provides the benefits ofsubstantial planarization of the solder balls using a simple,inexpensive, and easily maintainable system.

It should be noted that the compression force that flattens the outersurfaces 16 a of the solder balls can be generated in many differentways. FIG. 8, for example, shows an alternate embodiment of aplanarization apparatus 500 having a pressure plate 532 engaged againstthe bumped die 10 a opposite from the planarization chuck 402. Apressurizable vessel 534 is positioned above the pressure plate 532, anda fixed wall 536 is positioned over the pressurizable vessel 534. As thepressurizable vessel 534 is inflated, the pressure in the vessel forcesthe pressure plate 532 downward against the bumped die 10 a, compressingthe solder balls 12 against the flat surface 404 and flattening theouter surfaces 16 a.

In another embodiment, the pressure plate 532 is removed, and thepressurizable vessel 534 engages the bumped die 10 a directly to applythe compression force. Alternately, the compression force could begenerated by any number of devices which are commonly known in theindustry, including, for example, a press, a motor and mechanicallinkage, or other devices.

FIG. 9 is a side elevational view of yet another embodiment of aplanarization apparatus 600 in accordance with the invention. In thisembodiment, the planarization apparatus 600 includes a planarizationchuck 602 having a substantially flat surface 604, and a centrifuge 610.A pair of securing members (or clips) 606 engage and secure the bumpeddevice 10 a in position on the planarization chuck 602 with the solderballs 12 of the bumped device 10 a engaged with the flat surface 604.

In operation, the centrifuge 610 is rotated as depicted by arrow R. Therotation of the centrifuge generates a centrifugal force that compressesthe bumped device 10 a against the planarization chuck 602. Duringacceleration (and deceleration) of the centrifuge 610, the securingmembers 606 secure the bumped device 10 a in position on theplanarization chuck 602. As the rotational velocity of the centrifuge610 increases, a centrifugal force begins to press some or all of thesolder bumps 12 into the flat surface 604, substantially flattening theouter surfaces 16 a against the flat surface 604. As shown in FIG. 8,one or more planarization chucks 602 may be disposed within thecentrifuge 610 for simultaneously planarizing more than one bumpeddevice 10 a. The centrifuge 610 advantageously eliminates the use ofweights, pressurization vessels, or other devices used to generate thecompression force.

FIG. 10 shows a partial cross-sectional view of still another embodimentof a planarization apparatus 700 in accordance with the invention. Inthis embodiment, the planarization apparatus 700 includes a receptacle702 having a retaining wall 704. The retaining wall 704 partiallyencloses a receiving space 706 that is sized to receivably engage thebumped device 10. With the bumped device 10 placed in an invertedposition within the receiving space 706, the retaining wall 704 projectsabove the outer surfaces 16 b of the tallest solder bumps 12 (shown indashed lines). A protective layer 740 is disposed on the bumped device10 within the receiving space 706, the protective layer 740 at leastpartially surrounding and encasing the solder bumps 12. The protectivelayer 740 includes an upper surface 707. A reactive solution 750 isdisposed within the receiving space 706 on the upper surface 707 of theprotective layer 740, and a planarization gauge 109 is positionedproximate the receptacle 702.

In operation, the protective layer 740 is formed so that its thicknessis approximately equal to the height of the shortest solder bump 12. Theupper surface 707 thereby defines a seating plane through which theouter surfaces 16 b project. The reactive solution 750 is then depositedinto the receiving space 706 to chemically react with and dissolve (i.e.etch) the outer surfaces 16 b of the solder bumps 12. The protectivelayer 740 is comprised of one or more materials that are resistive orinert to the reactive solution 750. As the reactive solution 750 etchesthe projecting portion of the outer surfaces 16 b, the planarizationgauge 109 monitors a planarization condition of the seating plane andouter surfaces (as discussed above). When the outer surfaces 16 a aresubstantially planar with the upper surface 707, the reactive solution750 is removed. The protective layer 740 is then etched or dissolvedusing a suitable solution or other process (e.g. by heating) thatremoves the protective layer but does not harm the solder bumps 12. Theheights of the solder bumps 12 on the bumped device 10 are therebysubstantially planarized.

Suitable reactive solutions 750 for etching the solder balls 12 areknown, and include, for example, ammonium bifluoride/peroxide,nitric/ferric nitrate acid, nitric/hydrofluoric acid, or a two-stepcombination of nitric acid followed by ferric chloride. Similarly,suitable materials for the protective layer 740 are widely known.

The planarization gauge 109 could be incorporated into the receptacle702, such as by being disposed within the retaining wall 704.Alternately, by proper control or calibration of the reactive solution750 and/or the solder composition, the planarization gauge 109 may beeliminated.

In an alternate embodiment, the bumped device 10 is re-positioned withthe solder bumps 12 projecting downwardly, and the reactive solution 750is contained in a vat or reservoir below the bumped device 10. Using asuitable securing element, the bumped device 10 could be controllablylowered (or the reservoir of reactive solution raised) until some or allof the outer surfaces 16, but at least the outer surfaces 16 b of thetallest solder bumps, come into contact with the reactive solution 750.The reactive solution 750 then etches and dissolves the outer surfacesthat come into contact with the reactive solution, dissolving the outersurfaces and substantially planarizing the solder bumps.

In this embodiment, the protective layer 740, the retaining wall 704,and the planarization gauge 109 may be eliminated. Thus, the benefits ofsubstantial planarization of the solder balls 12 are achieved using arelatively simple, easily maintainable planarization system.

The above-described embodiments of planarization apparatus, and theirequivalents, provide improved testing, manufacture, and packaging ofbumped devices by substantially planarizing the outer surfaces of thesolder balls. By substantial planarization of the solder bumps, thecompression forces needed to engage the solder balls 12 into contactwith the contact pads 18 or a test interposer, printed circuit board, orother bumped device are substantially reduced or eliminated, therebyimproving reliability and avoiding damage to the bumped device.Expensive alternatives, such as micro-spring contact pads, areeliminated. Another advantage is that substantial planarization of thesolder balls improves the engagement of the bumped device with a devicehaving pedestal or protruding contacts, simplifying the manufacturingand reducing the cost of such devices.

The detailed descriptions of the above embodiments are not exhaustivedescriptions of all embodiments contemplated by the inventor to bewithin the scope of the invention. Indeed, persons skilled in the artwill recognize that certain elements of the above-described embodimentsmay variously be combined or eliminated to create further embodiments,and such further embodiments fall within the scope and teachings of theinvention. It will also be apparent to those of ordinary skill in theart that the above-described embodiments may be combined in whole or inpart to create additional embodiments within the scope and teachings ofthe invention.

Thus, although specific embodiments of, and examples for, the inventionare described herein for illustrative purposes, various equivalentmodifications are possible within the scope of the invention, as thoseskilled in the relevant art will recognize. The teachings providedherein of the invention can be applied to other apparatus and methodsfor substantial planarization of solder bumps, and not just to theapparatus and methods described above and shown in the figures. Ingeneral, in the following claims, the terms used should not be construedto limit the invention to the specific embodiments disclosed in thespecification and the claims, but should be construed to include allapparatus and methods that operate under the claims to providesubstantially planarized solder bumps. Accordingly, the invention is notlimited by the foregoing disclosure, but instead its scope is to bedetermined by the following claims.

What is claimed is:
 1. An apparatus for substantially planarizing aplurality of outer surfaces of an array of solder bumps attached to abumped device, comprising: a planarization member engageable with atleast some of the plurality of outer surfaces, the planarization memberapplying a planarization action on one or more of the plurality of outersurfaces to substantially planarize the solder bumps; a securing elementengageable with the bumped device to securely position the bumped deviceduring engagement of the planarization member with the outer surfaces;and a load device engageable with at least one of the bumped device orthe planarization member to urge the at least some outer surfaces of thebumped device into engagement with the planarization member, wherein thesecuring element includes a retaining clip engageable with a substrateof the bumped device and the planarization member includes asubstantially flat surface in contact with the at least some outersurfaces, the load device including a centrifuge engageable with theplanarization member, the planarization action comprising a centrifugalforce that compresses and mechanically flattens the one or more outersurfaces against the flat surface.
 2. The apparatus of claim 1, furthercomprising a planarization gauge engageable with at least a portion ofthe outer surfaces to assess a planarization condition of the solderbumps.
 3. The apparatus of claim 1 wherein the at least some outersurfaces engageable by the planarization member include the one or moreouter surfaces upon which the planarization action is applied.
 4. Anapparatus for approximately planarizing a plurality of solder bumps,comprising: a planarization member engageable with at least some of theplurality of solder bumps to apply a planarization action on one or moreof the plurality of solder bumps to approximately equalize the heightsof the solder bumps on a bumped device; a securing element engageablewith the bumped device to securely position the bumped device duringengagement of the planarization member with the solder bumps; and a loaddevice engageable with at least one of the bumped device or theplanarization member to urge the at least some solder bumps of thebumped device into engagement with the planarization member, wherein thesecuring element includes a retaining clip engageable with a substrateof the bumped device and the planarization member includes asubstantially flat surface in contact with the at least some solderbumps, the load device including a centrifuge engageable with theplanarization member, the planarization action comprising a centrifugalforce that compresses and mechanically flattens the one or more solderbumps against the flat surface.
 5. The apparatus of claim 4, furthercomprising a planarization gauge engageable with at least a portion ofthe solder bumps to assess a planarization condition of the solderbumps.
 6. The apparatus of claim 4 wherein the at least some solderbumps engageable by the planarization member include the one or moresolder bumps upon which the planarization action is applied.